Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.77   6.589%   $260.8979   $260.90   $260.90   $260.90  
  Purchase #2 $206.79   9.338%   $226.1001   $226.10   $226.10   $226.10  
  Purchase #3 $158.68   13.635%   $180.316   $180.32   $180.30   $180.30  
  Purchase #4 $177.65   12.807%   $200.4016   $200.40   $200.40   $200.40  
  Purchase #5 $216.86   10.809%   $240.3004   $240.30   $240.30   $240.30  
  Purchase #6 $123.49   12.302%   $138.6817   $138.68   $138.70   $138.70  
  Purchase #7 $68.27   4.198%   $71.136   $71.14   $71.15   $71.10  
  7 purchase totals = $1,196.51       $1,317.8337   $1,317.84   $1,317.85   $1,317.80